Systemic Lupus Erythematosus (SLE) is a chronic, multi-organ autoimmune disease. Neuropsychiatric manifestations, including neurologic (central or peripheral), psychiatric, and cognitive disturbances, have been reported to range from 14 to 75% in SLE patients. The determination of central nervous system (CMS) involvement has been based on manifestations ranging from overt disturbances such as seizure, stroke,or psychosis, to diffuse and more questionable CMSdisturbances, such as mild mood disorder, headache,and subtle cognitive deficits. The pathogenesis of these latter more subtle and diffuse manifestations is unknown and the diagnosis of CMS involvement remains problematic. More recently, "CMS" SLE has been used to describe only those patients with overt CMSdisturbances, while all others are categorized as "Non-CNS" SLE. Regardless of the classification criteria used to determine neuropsychiatric and/or CMS involvement in SLE, cognitive disturbances have been reported in up to 80% of patients with SLE when mild impairment is included. The most frequently reported deficits are in the areas of attention, speed of information processing, learning, and working memory (WM). The primary objective of this proposal is to examine the underlying pathophysiology of CMS involvement in the cognitive disturbances seen in SLE patients without overt CNS manifestations (e.g. stroke, seizure, psychosis). SLExpatientswill be studied using: (1) event-related brain potentials (ERPs) to obtain indices of brain function;(2) conventional and unconventional quantitative magnetic resonance imaging (MRI) to obtain indices of anatomic pathology;and (3) neuropsychological(NP) measures to determine the pattern of cognitive deficits in these patients. The NP battery will be composed of multiple tests grouped into cognitive domains, with particular emphasis on attention, WM, andprocessing speed. The ERP measures will be obtained from two paradigms that are sensitive to the WM components of encoding, maintenance, manipulation, and matching/response selection. MRI measures will focus on magnetization transfer ratio (MTR) to quantify tissue loss and microscopic tissue injury. The roles of active and inactive disease, medication use, and psychological factors will be carefully considered. Healthy control participants will also be studied. It is hypothesized that in patients with "Non-CNS" SLE, MRI (particularly MTR), and ERP (amplitude, latency, condition-related scalp topography, and single trial latency variability) will be sensitive indices of the cognitive deficits seen in SLE. The ability to define more clearly the information processing deficits seen in SLE and the underlying anatomical and functional basis of these deficits, will further the understanding of possible pathophysiological mechanisms of this disorder and lead to improved classification and treatment.